The present invention is directed to a new apparatus and method of charge distribution analysis, or CDA, to measure surface and/or subsurface charge layers, the sign of dominant charge carriers, and their mobility in--as well as the dielectric constant of--insulating and semiconducting dielectric materials.
The existence of surface/subsurface charge layers has been theoretically predicted on the basis of fundamental thermodynamic laws, specifically for ionic insulators. For instance, discussions of such charge layers may be found in the following articles: K. Lehovec, J. Chem. Phys. 21, 1123 (1953); K. L. Kliewer and J. S. Koehler, Phys. Rev. 140A, 1226 (1965); and W. D. Kingery, J. Am. Ceram. Soc. 57, 1 (1974) and 57, 74 (1974). A discussion of oxide insulators with electronic defects is found in the article by B. V. King and F. Freund, Phys. Rev. B29, 5814 (1984). The presence of such charge layers has been concluded from a variety of indirect observations such as the preferred segregation of certain aliovalent cations to surfaces and/or grain boundaries (Kingery 1974 articles cited above), the deflection of low energy electron or ion beams from surfaces, the energy dispersion of photoelectrons emitted from surfaces and many manifestations of electrostatic adhesion. Each of the above references is hereby incorporated herein by reference.
However, no method has existed until now for directly measuring and quantifying surface/subsurface charge layers, and for determining the sign and mobility of the dominant charge carriers.
Prior methods such as the measurement of cation surface or gain boundary segregation in ceramics are indirect and limited to high temperatures. They require thermal pretreatment of the samples, extensive sample preparation for observation of frozen-in disequilibrium states by microanalytical techniques (Kingery 1974) or extremely clean surface conditions in ultrahigh vacuum. Prior methods such as the deflection or energy dispersion of low energy charged beams, both electrons and other particles, inherently require high or ultrahigh vacua, and are restricted to very thin surface/subsurface layers due to the limited depth of penetration or escape depth of low energy electron or ion beams.
Prior methods such as based on electrostatic adhesion are qualitative at best, giving no or very limited information about the strength of the effect, about the concentration and the nature of the dominant charge carriers.